Piezoelectric ceramic composition, its production method, and piezoelectric device and dielectric device

ABSTRACT

This invention provides a piezoelectric ceramic composition that does not contain lead, can be sintered at a normal pressure and is excellent in at least one of a piezoelectric constant, an electromechanical coupling coefficient, a dielectric loss, a relative dielectric constant and a Curie point, its production method, and a piezoelectric device and a dielectric device each utilizing the piezoelectric ceramic composition. The invention relates to a piezoelectric composition expressed by the general formula {Li x (K 1-y Na y ) 1-x }(Nb 1-z Sb z )O 3 , each of x, y and z respectively falling within composition ranges of 0≦x≦0.2, 0≦y≦1.0 and 0≦z≦0.2 (with the exception of x=z=0), and its production method. The invention further relates to a piezoelectric device having a piezoelectric body formed of the piezoelectric ceramic composition described above and a dielectric device having a dielectric body formed of the piezoelectric ceramic composition described above.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to a piezoelectric ceramic composition notcontaining lead in the composition, its production method, and apiezoelectric device and a dielectric device each using thepiezoelectric ceramic composition as its material.

[0003] 2. Description of the Related Art

[0004] A PZT (PbTiO₃—PbZrO₃) component system ceramic containing leadhas been used in the past as a piezoelectric ceramic composition.

[0005] The PZT described above is excellent in an electro-mechanicalcoupling coefficient and piezoelectric characteristics such as apiezoelectric constant, and a piezoelectric device utilizing PZT hasbeen widely used in sensors, actuators, filters, and so forth. Since PZThas a relatively high relative dielectric constant, it has also beenused as a dielectric device such as in capacitors.

[0006] Though having excellent characteristics, the piezoelectricceramic composition formed of PZT contains lead as one of itsconstituent elements. Therefore, detrimental lead is likely to elutefrom industrial wastes of products containing PZT and to induceenvironmental pollution. Concerns about the environment in recent yearshave made it difficult to produce those products that may result in theenvironmental pollution, such as PZT. Therefore, development ofpiezoelectric ceramic compositions not containing lead has beenrequired, and a piezoelectric ceramic composition expressed by thegeneral formula (K_(1-x)Na_(x))Nbo₃ (with the proviso that 0<x<1) hasdrawn an increasing attention (“Journal of the American CeramicsSociety”, 1962, Vol. 45, No. 5, p209).

[0007] However, because sintering of the piezoelectric ceramiccomposition expressed by the general formula (K_(1-x)Na_(x)) NbO₃ (withthe proviso that 0<x<1) described above is difficult, hot-presssintering must be conducted and the production cost becomes high. Thepiezoelectric ceramic composition expressed by this general formulainvolves the problems that piezoelectric constants such as apiezoelectric d₃₁ constant and a piezoelectric g₃₁ constant and anelectromechanical coupling coefficient Kp are low, a dielectric loss isgreat and a relative dielectric constant is small. Therefore, though thepiezoelectric ceramic composition expressed by the general formula(K_(1-x)Na_(x)) NbO₃ (0<x<1) is believed to be a novel promisingcomposition that will replace PZT, it has hardly been put into practicalapplication. For this reason, the lead type piezoelectric ceramiccomposition such as PZT that may invite the environmental pollution hasstill been utilized widely at present even after the piezoelectricceramic composition expressed by the general formula described above hasbeen developed.

SUMMARY OF THE INVENTION

[0008] In view of the problems described above, this invention aims atproviding a piezoelectric ceramic composition that does not containlead, can be sintered at a normal pressure and is excellent in at leastone of a piezoelectric constant, an electromechanical couplingcoefficient, a dielectric loss, a relative dielectric constant and aCurie point, its production method, and a piezoelectric device and adielectric device each utilizing the piezoelectric ceramic composition.

[0009] According to a first aspect of the invention, there is provided apiezoelectric ceramic composition expressed by the general formula{Li_(x)(K_(1-y)Na_(y))_(1-x)}(Nb_(1-z)Sb_(z))O₃, each of x, y and zfalling within composition range of 0≦x≦0.2, 0≦y≦1.0 and 0≦z≦0.2 (withthe exception of x=z=0).

[0010] The piezoelectric ceramic composition according to the inventionis expressed by the general formula{Li_(x)(K_(1-y)Na_(y))_(1-x)}(Nb_(1-z)Sb_(z))O₃ and does not containlead in the composition.

[0011] Therefore, detrimental lead does not elute from wastes of thispiezoelectric ceramic composition to the natural world, and thecomposition is safe.

[0012] In the general formula given above, each of x, y and z existswithin the respective range described above. Therefore, thepiezoelectric ceramic composition is excellent in at least one of apiezoelectric constant, an electromechanical coupling coefficient, adielectric loss, a relative dielectric constant and a Curie point. Thepiezoelectric ceramic composition described above can be sufficientlydensified through sintering at a normal pressure.

[0013] The piezoelectric ceramic composition is safe to the environment,can be sintered at a normal temperature and can be used as a material ofa piezoelectric device or dielectric device having high performance.

[0014] Incidentally, the term “piezoelectric ceramic composition” usedin the invention includes not only ceramic compositions havingpiezoelectric characteristics but also dielectric ceramic compositionshaving dielectric characteristics.

[0015] According to a second aspect of the invention, there is provideda method of producing a piezoelectric ceramic composition comprising thesteps of molding powder of a piezoelectric ceramic composition expressedby the general formula {Li_(x)(K_(1-y)Na_(y))_(1-x)}(Nb_(1-z)Sb_(z))O₃,each of x, y and z falling within composition range of 0≦x≦0.2, 0≦y≦1.0and 0≦z≦0.2 (with the exception of x=z=0); and sintering the resultingmolding.

[0016] The molding obtained by molding powder formed of thepiezoelectric ceramic composition described above can be sintered at anormal temperature. Therefore, sintering can be carried out easily andat a low cost. The piezoelectric ceramic composition obtained aftersintering does not contain lead and is excellent in at least one ofpiezoelectric constants such as a piezoelectric d₃₁ constant and apiezoelectric g₃₁ constant, an electromechanical coupling coefficient, adielectric loss, a relative dielectric constant and a Curie point.Therefore, the piezoelectric ceramic composition can be utilized as amaterial of high-performance piezoelectric or dielectric devices.

[0017] According to a third aspect of the invention, there is provided amethod of producing a piezoelectric ceramic composition comprising thesteps of mixing a lithium-containing compound, a sodium-containingcompound, a potassium-containing compound, a niobium-containing compoundand an antimony-containing compound; and sintering the mixture.

[0018] In the invention, the lithium-containing compound, thesodium-containing compound, the potassium-containing compound, theniobium-containing compound and the antimony-containing compound aremixed and sintered as described above.

[0019] In consequence, the piezoelectric ceramic composition expressedby the general formula {Li_(x)(K_(1-y)Na_(y))_(1-x)}(Nb_(1-z)Sb_(z))O₃can be easily obtained.

[0020] When sintering is conducted, the piezoelectric ceramiccomposition described above can be sintered at the normal temperature.The piezoelectric ceramic composition obtained after sintering does notcontain lead and is excellent in at least one of the piezoelectricconstants such as a piezoelectric d₃₁ constant and a piezoelectric g₃₁constant, an electromechanical coupling coefficient, a dielectric loss,a relative dielectric constant and a Curie point.

[0021] Next, according to a fourth aspect of the invention, there isprovided a piezoelectric device having a piezoelectric body formed ofthe piezoelectric ceramic composition of the first invention describedabove.

[0022] The piezoelectric device described above has a piezoelectric bodyformed of the piezoelectric ceramic composition of the first invention.Therefore, the piezoelectric device does not contain lead and is safe tothe environment. The piezoelectric device can utilize as such theproperties of the piezoelectric ceramic composition in that thepiezoelectric constant, the electro-mechanical coupling coefficient,etc, are high. Therefore, the piezoelectric device can be utilized asexcellent piezoelectric devices such as a piezoelectric sensor having ahigh sensitivity, a piezoelectric vibrator and an actuator having highelectromechanical energy conversion efficiency.

[0023] According to a fifth aspect of the invention, there is provided adielectric device having a dielectric body formed of the piezoelectricceramic composition of the first invention.

[0024] The dielectric device described above has the dielectric bodyformed of the piezoelectric ceramic composition of the first invention.Therefore, the dielectric device does not contain lead and is safe tothe environment. The dielectric device can utilize as such theproperties of the piezoelectric ceramic composition in that thedielectric loss is low and the relative dielectric constant is high.Consequently, the dielectric device can be utilized as excellentdielectric devices such as a capacitor having a large electrostaticcapacity.

[0025] According to a sixth aspect of the invention, there is provided apiezoelectric device having a piezoelectric body formed of apiezoelectric ceramic composition produced by the production method ofthe second or third invention.

[0026] The piezoelectric device of the invention uses the piezoelectricceramic composition produced by the production method of the second orthird invention as the piezoelectric body. Therefore, the piezoelectricdevice can as such utilize the excellent characteristics of thepiezoelectric ceramic composition, and can be utilized as excellentpiezoelectric devices such as a piezoelectric sensor having a highsensitivity, a piezoelectric vibrator and an actuator having highelectro-mechanical energy conversion efficiency.

[0027] According to a seventh aspect of the invention, there is provideda dielectric device having a dielectric body formed of a piezoelectricceramic composition produced by the production method of a piezoelectricceramic composition according to the second or third invention.

[0028] The dielectric device described above uses the piezoelectricceramic composition produced by the production method of a piezoelectricceramic composition according to the second or third invention as thedielectric body. Therefore, the dielectric device can utilize as suchthe excellent properties of the piezoelectric ceramic composition asexcellent dielectric devices such as a capacitor having a largeelectrostatic capacity.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] In the present invention, the piezoelectric ceramic compositiondescribed above is expressed by the general formula{Li_(x)(K_(1-y)Na_(y))_(1-x)}(Nb_(1-z)Sb_(z))O₃, and each of x, y and zis within the composition range of 0≦x≦0.2, 0≦y≦0.8 and 0≦z≦0.2 (withthe exception of x=z=0), respectively.

[0030] Here, when x>0.2, y>1.0 and z>0.2 or when x and z aresimultaneously 0 (x=z=0), the piezoelectric constant, theelectro-mechanical coupling coefficient and the relative dielectricconstant of the piezoelectric ceramic composition drop or the dielectricloss becomes great with the result that a piezoelectric ceramiccomposition having desired piezoelectric and dielectric characteristicscannot be obtained.

[0031] The piezoelectric ceramic composition described above has bothpiezoelectric and dielectric properties and can be used as bothpiezoelectric body and dielectric body. More concretely, it can be usedas piezoelectric vibrators, surface wave filters, piezoelectric sensors,actuators, ultrasonic motors, piezoelectric transformers and capacitors.

[0032] In the first invention described above, the piezoelectric ceramiccomposition preferably has a piezoelectric d₃₁ constant of at least 30pm/v.

[0033] In this case, the piezoelectric ceramic composition can be usedin sensors, ultrasonic motors, actuators, piezoelectric transformers,piezoelectric vibrators, etc, having a high sensitivity by making themost of its high piezoelectric d₃₁ constant of at least 30 pm/V. Tofurther improve the sensitivity, the piezoelectric d₃₁ constant isparticularly preferably at least 50 pm/V.

[0034] The piezoelectric ceramic composition preferably has apiezoelectric g₃₁ constant of at least 7×10⁻³ Vm/N.

[0035] In this case, the piezoelectric ceramic composition can be usedas piezoelectric transformers, ultrasonic motors, sensors, etc, having ahigh boltage boosting ratio by making the most of its high piezoelectricg₃₁ constant of at least 7×10⁻³ Vm/N. To obtain products having a higherboosting ratio, the piezoelectric g₃₁ constant is particularlypreferably at least 10×10⁻³ Vm/N.

[0036] The piezoelectric ceramic composition described above preferablyhas an electromechanical coupling coefficient Kp of at least 0.3.

[0037] In this case, the piezoelectric ceramic composition can be usedas piezoelectric actuators, piezoelectric vibrators, sensors,piezoelectric transformers, ultrasonic motors, etc, having highconversion efficiency of mechanical energy and electric energy by makingthe most of its high electromechanical coupling coefficient Kp of atleast 0.3. To further improve conversion efficiency of mechanical energyand electric energy, the electromechanical coupling coefficient Kp isparticularly preferably at least 0.35.

[0038] The piezoelectric ceramic composition described above preferablyhas a dielectric loss of not greater than 0.09.

[0039] In this case, the piezoelectric ceramic composition can be usedas dielectric devices such as capacitors, piezoelectric transformers,ultrasonic motors, etc, by making the most of its low dielectricconstant of not greater than 0.09. Incidentally, the dielectric loss isparticularly preferably 0.035 or less.

[0040] The piezoelectric ceramic composition described above preferablyhas a relative dielectric constant of at least 400.

[0041] In this case, the piezoelectric ceramic composition can be usedas dielectric devices such as capacitors having a great electrostaticcapacity by making the most of its relative dielectric constant of atleast 400.

[0042] The piezoelectric ceramic composition described above preferablyhas a Curie point of at least 200° C.

[0043] In this case, the piezoelectric ceramic composition can be usedunder a high temperature environment such as in the proximity of anautomobile engine by making the most of its high Curie point of at least200° C. Incidentally, the Curie point is particularly preferably atleast 250° C.

[0044] The piezoelectric ceramic composition described above preferablyhas a piezoelectric d₃₁ constant of at least 30 pm/V, anelectromechanical coupling coefficient Kp of at least 0.3 and a Curiepoint of at least 200° C.

[0045] In this case, the piezoelectric ceramic composition can be usedunder a high temperature environment such as in the proximity of anautomobile engine, and can be used as sensors, piezoelectric actuators,piezoelectric transformers, ultrasonic motors, etc, having highsensitivity and high conversion efficiency of mechanical energy andelectric energy.

[0046] The piezoelectric ceramic composition described above preferablyhas a piezoelectric d₃₁ constant of at least 30 pm/v, a dielectricconstant of not greater than 0.09 and a Curie point of at least 200° C.

[0047] In this case, the piezoelectric ceramic composition can be usedunder a high temperature environment such as in the proximity of anautomobile engine, and can be used as piezoelectric transformers,ultrasonic motors, etc, having high sensitivity and excellent dielectricloss.

[0048] Next, in the third invention described above, it is preferredthat the lithium-containing compound is Li₂CO₃, the sodium-containingcompound is Na₂CO₃, the potassium-containing compound is K₂CO₃, theniobium-containing compound is Nb₂o₅ and the antimony-containingcompound is Sb₂O₅ or Sb₂O₃.

[0049] In this case, the piezoelectric ceramic composition describedabove can be easily produced.

[0050] In the fourth or sixth invention, examples of the piezoelectricdevices described above include piezoelectric vibrators, surface wavefilters, piezoelectric sensors, actuators, ultrasonic motors,piezoelectric transformers, piezoelectric gyro sensors, knock sensors,and so forth.

[0051] Next, in the fifth or seventh invention, the dielectric devicesdescribed above are for example capacitors and stacked capacitors.

EXAMPLE 1

[0052] Piezoelectric ceramic compositions according to examples of theinvention will be explained.

[0053] In this example, the piezoelectric ceramic composition describedabove is produced, and its characteristics such as piezoelectric anddielectric characteristics are measured.

[0054] The piezoelectric ceramic composition is expressed by the generalformula {Li_(x)(K_(1-y)Na_(y))_(1-x)}(Nb_(1-z)Sb_(z))O₃, and each of x,y and z is within the composition range of 0≦x≦0.2, 0≦y≦1.0 and 0≦z≦0.2,respectively (with the exception of x=z=0).

[0055] Next, a method for producing the piezoelectric ceramiccomposition of this example will be explained.

[0056] First, high purity Li₂CO₃, K₂CO₃, Na₂CO₃, Nb₂O₅ and Sb₂O₅ eachhaving a purity of at least 99% are prepared as the starting materialsof the piezoelectric ceramic composition. A plurality of materials isprepared by use of these starting materials by changing x and z butkeeping y at 0.5 in the general formula{Li_(x)(K_(1-y)Na_(y))_(1-x)}(Nb_(1-z)Sb_(z))O₃. Here, x is set to 0,0.02, 0.04, 0.06, 0.08, 0.10, 0.12, 0.15 and 0.20. On the other hand, zis set to 0, 0.02, 0.04, 0.06, 0.08, 0.10, 0.12, 0.15 and 0.20. Thestarting materials so blended as to achieve each stoichiometriccomposition are mixed in acetone for 24 hours by use of a ball mill toprepare a mixture of each stoichiometric composition.

[0057] Next, the mixture is calcined at 750° C. for 5 hours, and themixture after calcinations is pulverized for 24 hours in the ball mill.Subsequently, polyvinyl butyral as a binder is added and the mixture isgranulated.

[0058] Powder after granulation is press-molded at a pressure of 2tons/cm² into a disc having a diameter of 18 mm and a thickness of 1 mm,and the resulting molding is sintered at 1,000 to 1,300° C. for onehour. The sintering temperature at this time is selected between 1,000°C. and 1,300° C. to a temperature that provides a maximum density. Eachmolding after sintering is compacted to a relative density of at least98%.

[0059] Both surfaces of each molding after sintering arestraight-polished and disc polished. Gold electrodes are then providedto both surfaces of each disc sample by sputtering. A DC voltage of 1 to5 kV/mm is applied across the electrodes, in silicone oil, at 100° C.for 10 minutes, and polarization is attained in the direction ofthickness to give each piezoelectric ceramic composition of thisexample.

[0060] The piezoelectric d₃₁ constant, the piezoelectric g₃₁ constant,the electromechanical coupling coefficient Kp, the Curie point, thedielectric loss and the relative dielectric constant are measured foreach of the piezoelectric ceramic compositions so produced in thisexample. Here, the piezoelectric d₃₁ constant, the piezoelectric g₃₁constant and the electro-mechanical coupling coefficient Kp are measuredin accordance with a resonance-antiresonance method by use of animpedance analyzer. The dielectric loss and the relative dielectricconstant are measured at a measurement frequency of 1 kHz by use of theimpedance analyzer. The Curie point is set to the temperature thatprovides the highest relative dielectric constant.

[0061] The results are shown in Tables 1 to 6. TABLE 1 piezoelectric d₃₁constant (pm/V) x 0.20 9.7 24.5 9.1 24.3 33.9 44.5 0.15 10.1 26.2 51.046.4 44.2 34.7 0.12 55.8 58.2 66.4 0.10 20.4 51.1 63.9 65.4 91.6 84.573.4 26.9 22.7 0.08 27.5 62.8 72.7 78.1 75.1 82.2 50.8 82.0 0.06 57.759.2 102.9 87.6 77.8 80.1 41.3 0.04 39.8 55.2 60.3 74.0 66.9 59.9 61.50.02 46.9 51.5 56.3 65.5 74.8 66.2 0 (37.6) 45.1 63.0 58.3 54.8 60.937.7 28.2 0 0.02 0.04 0.06 0.08 0.10 0.12 0.15 0.20 z

[0062] TABLE 2 electro-mechanical coupling coefficient Kp x 0.20 0.0920.148 0.033 0.162 0.240 0.285 0.15 0.087 0.189 0.348 0.309 0.279 0.2030.12 0.340 0.357 0.361 0.10 0.151 0.357 0.402 0.390 0.459 0.433 0.3780.120 0.150 0.08 0.196 0.400 0.425 0.421 0.419 0.403 0.236 0.415 0.060.332 0.441 0.506 0.448 0.420 0.409 0.236 0.04 0.371 0.489 0.463 0.4680.422 0.321 0.351 0.02 0.469 0.435 0.480 0.473 0.473 0.334 0 (0.334)0.418 0.466 0.386 0.328 0.260 0.233 0.134 0 0.02 0.04 0.06 0.08 0.100.12 0.15 0.20 z

[0063] TABLE 3 piezoelectric g₃₁ constant (mVm/N) x 0.20 2.8 3.0 0.7 3.44.8 5.6 0.15 1.4 4.4 7.3 6.1 6.0 4.1 0.12 6.1 6.4 5.9 0.10 3.5 7.7 7.87.2 7.9 7.2 6.0 1.5 3.1 0.08 4.7 8.0 8.3 7.4 7.3 6.4 4.6 0.06 7.5 5.48.6 7.4 7.4 7.0 4.1 0.04 11.0 14.0 13.0 9.6 8.8 5.8 0.02 14.5 10.2 12.510.7 9.3 5.2 0 (9.9) 12.2 10.4 7.8 6.8 3.6 4.2 2.0 0 0.02 0.04 0.06 0.080.10 0.12 0.15 0.20 z

[0064] TABLE 4 Curie point (° C.) x 0.20 505 483 462 440 421 400 0.15502 469 440 403 375 345 0.10 499 471 443 400 355 277 276 275 0.08 485448 414 373 333 258 0.06 474 425 385 346 312 238 0.04 460 406 365 328288 215 0.02 435 388 344 311 280 205 0 (415) 370 326 294 259 193 177 160 0 0.02 0.04 0.06 0.08 0.10 0.15 0.20 z

[0065] TABLE 5 relative dielectric constant x 0.20 399 925 739 817 792902 0.15 530 675 786 864 830 950 0.12 1101 1272 0.10 657 750 920 10331314 1320 1382 2023 829 0.08 657 887 986 1193 1166 1458 1237 1280 0.06864 904 1359 1339 1189 1298 1129 0.04 409 446 522 868 858 1159 1342 0.02364 408 510 692 907 1427 0 (429) 416 687 847 913 1898 1020 1595  0 0.020.04 0.06 0.08 0.10 0.12 0.15 0.20 z

[0066] TABLE 6 dielectric loss x 0.20 0.091 0.299 0.118 0.211 0.1800.030 0.15 0.045 0.173 0.023 0.071 0.105 0.082 0.12 0.018 0.020 0.0250.10 0.088 0.021 0.024 0.015 0.023 0.018 0.031 0.048 0.034 0.08 0.0370.013 0.016 0.016 0.022 0.027 0.034 0.06 0.050 0.026 0.020 0.029 0.0270.029 0.035 0.04 0.014 0.018 0.029 0.026 0.024 0.036 0.02 0.003 0.0250.035 0.028 0.030 0.040 0 (0.036) 0.051 0.107 0.053 0.037 0.046 0.0350.038 0 0.02 0.04 0.06 0.08 0.10 0.12 0.15 0.20 z

[0067] To clarify the excellent characteristics of the piezoelectricceramic composition of the invention, this example produces thecomparative products in the following way.

[0068] First, high purity K₂CO₃, Na₂CO₃ and Nb₂O₅ each having a purityof at least 99% are prepared as the starting materials of thecomparative products. The starting materials are blended into thestoichiometric composition of (K_(1-x)Na_(x))NbO₃ (with x=0.5), and thecomposition is mixed in acetone for 24 hours by use of a ball mill toprepare a mixture.

[0069] Next, this mixture is calcined at 750° C. for 5 hours, and themixture after calcination is pulverized for 24 hours in the ball mill.Subsequently, polyvinyl butyral is added as a binder, and the mixture isgranulated.

[0070] Powder after granulation is press-molded at a pressure of 2tons/cm² into a disc having a diameter of 18 mm and a thickness of 1 mm,and the resulting molding is sintered at 1,100° C. for one hour.Incidentally, a relative density after sintering is 96.2%.

[0071] Both surfaces of each molding after sintering arestraight-polished and disc-polished. Gold electrodes are then providedto both surfaces of each disc sample by sputtering. A DC voltage of 1 to5 kV/mm is applied across the electrodes for 10 minutes, in siliconeoil, at 100° C., and polarization is attained in the direction ofthickness to give each comparative product.

[0072] The piezoelectric d₃₁ constant, the piezoelectric g₃₁ constant,the electromechanical coupling coefficient Kp, the Curie point, thedielectric loss and the relative dielectric constant are measured foreach of the comparative product so produced. The measurement method ofeach measurement value is the same as that of the products of theinvention.

[0073] The results are shown in Tables 1 to 6. In the matrix shown ineach table, the column of x=0 and z=0 represents the measurement resultof the comparative products.

[0074] It can be seen from Table 1 that in the composition range of0≦x≦0.10, y=0.5 and 0≦z≦0.10 in the general formula{Li_(x)(K_(1-y)Na_(y))_(1-x)}(Nb_(1-z)Sb_(z))O₃, the piezoelectric d₃₁constant of almost all the piezoelectric ceramic compositions of thisexample is higher than the piezoelectric d₃₁ constant of the comparativeproducts. The piezoelectric d₃₁ constant scores the highest value of102.9 pm/v at x=0.06, y=0.5 and z=0.04.

[0075] When a charge detection type circuit or a current detection typecircuit is used, the piezoelectric d₃₁ constant is generallyproportional to an output voltage of a piezoelectric type sensor such asacceleration sensors, pressure application sensors, impact sensors andknock sensors. From this aspect, a piezoelectric ceramic compositionhaving a higher piezoelectric d₃₁ constant can fabricate a sensor havinga greater charge sensor output. To produce sensors havingcharacteristics at least equivalent to those of the comparativeproducts, the composition preferably has a piezoelectric d₃₁ constant ofat least 30 pm/v. To produce a high sensitivity sensor by improving asignal-to-noise ratio (SN ratio) and an output voltage, thepiezoelectric d₃₁ constant is preferably at least 50 pm/V.

[0076] Next, it can be seen from Table 2 that, in the composition rangeof 0≦x≦0.10, y=0.5 and 0≦z≦0.10 in the general formula{Li_(x)(K_(1-y)Na_(y))_(1-x)}(Nb_(1-z)Sb_(z))O₃, the electromechanicalcoupling coefficients Kp of almost all the piezoelectric ceramiccompositions of this example are higher than the electromechanicalcoupling coefficient Kp of the comparative products. Theelectromechanical coupling coefficient Kp scores the highest value of0.506 at x=0.06, y=0.5 and z=0.04.

[0077] The electromechanical coupling coefficient Kp is generallyproportional to electromechanical energy conversion efficiency ofpiezoelectric transformers, ultrasonic motors, actuators or ultrasonicvibrators. From this aspect, a piezoelectric ceramic composition havinga higher electromechanical coupling coefficient Kp can fabricatepiezoelectric transformers, ultrasonic motors, actuators or ultrasonicvibrators having higher electromechanical energy conversion efficiency.To produce piezoelectric transformers, ultrasonic motors, actuators orultrasonic vibrators having characteristics at least equivalent to thoseof the comparative products, the composition preferably has anelectromechanical coupling coefficient Kp of at least 0.3, morepreferably at least 0.35.

[0078] Next, it can be seen from Table 3 that, in the composition rangeof 0≦x≦0.04, y=0.5 and 0≦z≦0.06 in the general formula{Li_(x)(K_(1-y)Na_(y))_(1-x)}(Nb_(1-z)Sb_(z))O₃, the piezoelectric g₃₁constants of almost all the piezoelectric ceramic compositions of thisexample are higher than the piezoelectric g₃₁ constants of thecomparative products. The piezoelectric g₃₁ constants scores the highestvalue of 14.5×10⁻³ Vm/N at x=0.02, y=0.5 and z=0.

[0079] The piezoelectric g₃₁ constant is generally proportional to anoutput voltage of piezoelectric sensors, piezoelectric transformers andultrasonic motors in the same way as the piezoelectric d₃₁ constant.From this aspect, a piezoelectric ceramic composition having a higherpiezoelectric g₃₁ constant can fabricate a sensor having a greatercharge sensor output. To produce sensors having characteristics at leastequivalent to those of the comparative products, the compositionpreferably has a piezoelectric g₃₁ constant of at least 10×10⁻³ Vm/N.

[0080] Next, it can be seen from Table 4 that in the composition rangeof 0≦x≦0.20, y=0.5 and 0≦z≦0.10 in the general formula{Li_(x)(K_(1-y)Na_(y))_(1-x)}(Nb_(1-z)Sb_(z))O₃, the Curie points of thepiezoelectric ceramic compositions of this example is higher than 193°C. Therefore, the piezoelectric ceramic composition of this examplefalling within the composition range described above can be used forhigh-temperature sensor components, high-temperature actuator componentsand high-temperature ultrasonic motor components such as knock sensorsthat can be stably used for a long time at high-temperature portions inthe proximity of automobile engines.

[0081] To stably use the composition as the high-temperature sensorcomponents, the high-temperature actuator components and thehigh-temperature ultrasonic motor components for a longer time, theCurie point described above is preferably higher than 200° C. andfurther preferably higher than 250° C.

[0082] Next, it can be seen from Table 5 that in the composition rangeof 0≦x≦0.20, y=0.5 and 0≦z≦0.20 in the general formula{Li_(x)(K_(1-y)Na_(y))_(1-x)}(Nb_(1-z)Sb_(z))O₃, the relative dielectricconstants of almost all the piezoelectric ceramic compositions of thisexample are higher than the relative dielectric constants of thecomparative products. The relative dielectric constants scores thehighest value of 2,023 at x=0.10, y=0.5 and z=0.15.

[0083] The relative dielectric constant is generally proportional to theelectrostatic capacity of capacitors. From this aspect, a piezoelectricceramic composition having a higher relative dielectric constant canfabricate a capacitor having a greater electrostatic capacity. Toproduce capacitors having characteristics at least equivalent to thoseof the comparative products, the composition preferably has a relativedielectric constant of 400 or more, further preferably 600 or more.

[0084] Next, it can be seen from Table 6 that in the composition rangeof 0≦x≦0.20, y=0.5 and 0≦z≦0.20 in the general formula{Li_(x)(K_(1-y)Na_(y))_(1-x)}(Nb_(1-z)Sb_(z))O₃, the dielectric loss ofalmost all the piezoelectric ceramic compositions of this example isgreater than the dielectric loss of the comparative products. Thedielectric loss scores the highest value of 0.003 at x=0.02, y=0.5 andz=0.

[0085] The dielectric loss is proportional to the heat energy that acapacitor loses when an AC voltage is applied to the capacitor such as alaminated capacitor. From this aspect, a piezoelectric ceramiccomposition having a smaller dielectric loss can fabricate a capacitorhaving a smaller energy loss. To produce capacitors havingcharacteristics at least equivalent to those of the comparativeproducts, the composition preferably has a dielectric loss of notgreater than 0.09, further preferably not greater than 0.035.

EXAMPLE 2

[0086] In this example, piezoelectric ceramic compositions are preparedby changing the K and Na contents contained in the piezoelectric ceramiccompositions expressed by the general formula{Li_(x)(K_(1-y)Na_(y))_(1-x)}(Nb_(1-z)Sb_(z))O₃ described above, and thepiezoelectric and dielectric characteristics are examined.

[0087] More concretely, the piezoelectric ceramic compositions in whichy is 0.60, 0.50 and 0.40 are prepared while x and z are kept fixed atx=0.06 and z=0.04, respectively, in the general formula{Li_(x)(K_(1-y)Na_(y))_(1-x)}(Nb_(1-z)Sb_(z))O₃. Therefore, the Nacontent in this instance is 0.564 mol, 0.47 mol and 0.37.6 mol per molof the compounds expressed by the general formula given above.

[0088] Next, the production method of the piezoelectric ceramiccompositions described above will be explained.

[0089] First, high purity Li₂CO₃, K₂CO₃, Na₂CO₃, Nb₂O₅ and Sb₂O₅ eachhaving a purity of at least 99% are prepared as the starting materialsin the same way as in Example 1. The starting materials are blended insuch a fashion as to attain x=0.06, z=0.04 and y=0.60, 0.50 and 0.40,respectively, in the general formula{Li_(x)(K_(1-y)Na_(y))_(1-x)}(Nb_(1-z)Sb_(z))O₃ to prepare three kindsof materials. These three kinds of materials are respectively mixed inacetone for 24 hours by use of a ball mill in the same way as in Example1 and each mixture of the stoichiometric composition is prepared.

[0090] Each mixture is calcined and pulverized. After a binder is added,the mixture is granulated in the same way as in Example 1.

[0091] Powder after granulation is press-molded at a pressure of 2tons/cm² into a disc having a diameter of 18 mm and a thickness of 1 mm,and the resulting molding is sintered at 1,000 to 1,300° C. for one hourin the same way as in Example 1. Incidentally, a temperature providing amaximum density is selected as the sintering temperature between 1,000and 1,300° C. All the moldings after sintering are compacted to arelative density 98% or more.

[0092] Both surfaces of each molding after sintering arestraight-polished and disc-polished. Gold electrodes are then providedto both surfaces of each disc sample by sputtering. A DC voltage of 1 to5 kV/mm is applied across the electrodes for 10 minutes, in siliconeoil, at 100° C., and polarization is attained in the direction ofthickness to give three kinds of piezoelectric ceramic compositions.These compositions are called Sample E1 to Sample E3, respectively.

[0093] The piezoelectric ceramic composition of Sample E1 is expressedby Li_(0.06)(K_(0.4)Na_(0.6))_(0.94)(Nb_(0.96)Sb_(0.04))O₃. Thepiezoelectric ceramic composition of Sample E2 is expressed byLio_(0.06)(K_(0.5)Na_(0.5))_(0.94) (Nb_(0.96)Sb_(0.04))₃. Thepiezoelectric ceramic composition of Sample E3 is expressed byLi_(0.06)(K_(0.6)Na_(0.4))_(0.94) (Nb_(0.96)Sb_(0.04))O₃.

[0094] The piezoelectric d₃₁ constant, the piezoelectric g₃₁ constant,the electro-mechanical coupling coefficient Kp, the dielectric loss andthe relative dielectric constant are measured for these three kinds ofpiezoelectric ceramic compositions (Samples E1 to E3). Among them, thepiezoelectric d₃₁ constant, the piezoelectric g₃₁ constant and theelectro-mechanical coupling coefficient Kp are measured in accordancewith a resonance-antiresonance method using an impedance analyzer. Thedielectric loss and the relative dielectric constant are measured at ameasuring frequency of 1 kHz by use of the impedance analyzer.

[0095] The result is tabulated in Table 7. TABLE 7 sample No. Sample E1Sample E2 Sample E3 x 0.06 0.06 0.06 y 0.60 0.50 0.40 z 0.04 0.04 0.04piezoelectric d₃₁ 42.3 102.9 25.8 constant (pm/V) electro-mechanical0.248 0.506 0.176 coupling coefficient Kp piezoelectric g₃₁ 4.3 8.6 3.3constant (mVm/N) relative dielectric 1105 1359 876 constant dielectricloss 0.035 0.020 0.038

[0096] As can be seen from Table 7, these three kinds of piezoelectricceramic compositions of this example exhibit excellent piezoelectric anddielectric characteristics and have particularly excellent relativedielectric constants.

[0097] It can be understood from this example that when thepiezoelectric ceramic composition is produced by changing the y value inthe general formula {Li_(x)(K_(1-Y)NA_(y))_(1-x)}(Nb_(1-z)Sb_(z))O₃,piezoelectric ceramic compositions excellent in both piezoelectric anddielectric characteristics can be obtained.

What is claimed is:
 1. A piezoelectric ceramic composition expressed bythe general formula {Li_(x)(K_(1-y)Na_(y))_(1-x)}(Nb_(1-z)Sb_(z))O₃,each of x, y and z respectively falling within composition ranges of0≦x≦0.2, 0≦y≦1.0 and 0≦z≦0.2 (with the exception of x=z=0).
 2. Apiezoelectric ceramic composition as defined in claim 1, wherein apiezoelectric d₃₁ constant of said piezoelectric ceramic composition is30 pm/v or above.
 3. A piezoelectric ceramic composition as defined inclaim 1, wherein a piezoelectric g₃₁ constant of said piezoelectricceramic composition is 7×10⁻³ Vm/N or above.
 4. A piezoelectric ceramiccomposition as defined in claim 1, wherein an electromechanical couplingcoefficient Kp of said piezoelectric ceramic composition is 0.3 orabove.
 5. A piezoelectric ceramic composition as defined in claim 1,wherein a dielectric loss of said piezoelectric ceramic composition is0.09 or below.
 6. A piezoelectric ceramic composition as defined inclaim 1, wherein a relative dielectric constant of said piezoelectricceramic composition is 400 or above.
 7. A piezoelectric ceramiccomposition as defined in claim 1, wherein a Curie point of saidpiezoelectric ceramic composition is 200° C. or above.
 8. Apiezoelectric ceramic composition as defined in claim 1, wherein saiddielectric ceramic composition has a piezoelectric d₃₁ constant of 30pm/V or above, an electromechanical coupling coefficient Kp of 0.3 orabove and a Curie point of 200° C. or above.
 9. A piezoelectric ceramiccomposition as defined in claim 1, wherein said dielectric ceramiccomposition has a piezoelectric d₃₁ constant of 30 pm/v or above, adielectric loss of 0.09 or below and a Curie point of 200° C. or above.10. A method of producing a piezoelectric ceramic composition comprisingthe steps of: molding powder of a piezoelectric composition expressed bythe general formula {Li_(x)(K_(1-y)Na_(y))_(1-x)}(Nb_(1-z)Sb_(z))O₃,each of x, y and z respectively falling within composition range of0≦x≦0.2, 0≦y≦1.0 and 0≦z≦0.2 (with the exception of x=z=0); andsintering the resulting molding.
 11. A method of producing apiezoelectric ceramic composition for obtaining said piezoelectricceramic composition as defined in claim 1, comprising the steps of:mixing a lithium-containing compound, a sodium-containing compound, apotassium-containing compound, a niobium-containing compound and anantimony-containing compound; and sintering the mixture.
 12. A method ofproducing a piezoelectric ceramic composition as defined in claim 11,wherein said lithium-containing compound is Li₂CO₃, saidsodium-containing compound is Na₂CO₃, said potassium-containing compoundis K₂CO₃, said niobium-containing compound is Nb₂O, and saidantimony-containing compound is Sb₂O₅ or Sb₂O₃.
 13. A piezoelectricdevice having a piezoelectric body formed of said piezoelectric ceramiccomposition as defined in claim
 1. 14. A dielectric device having adielectric body formed of said piezoelectric ceramic composition asdefined in claim
 1. 15. A piezoelectric device having a piezoelectricbody formed of a piezoelectric ceramic composition produced by saidproduction method of a piezoelectric ceramic composition as defined inclaim
 10. 16. A dielectric device having a dielectric body formed of adielectric ceramic composition produced by said production method of apiezoelectric ceramic composition as defined in claim 10.